Vertebral prosthesis and spinal fixation system

ABSTRACT

A vertebral prosthesis and spinal fixation system includes a vertebral prosthesis having a height adjustable shaft and an anchoring mechanism coupled to the shaft. The system further includes a spinal fixation device and a number of bone screws. The bone screws attach the fixation device to the vertebral prosthesis via the anchoring mechanism.

FIELD OF THE INVENTION

The present invention relates to a vertebral prosthesis and relatedspinal fixation system. In particular, the present invention relates toa vertebral prosthesis that is designed to be used in conjunction with aspinal fixation plate.

BACKGROUND OF THE INVENTION

The spinal column is comprised of twenty-six interlocking vertebrae.These vertebrae are separated by disks. The spine provides load-bearingsupport for one-half of the body's mass and it protects the nerves ofthe spinal column. The disks provide shock absorption and facilitate thebending of the spine.

The combination of the vertebrae and disks at each vertebral segmentallows for motion of the spine, in particular, flexing, rotation andextension. The motion and support functions of the spine, in combinationwith the many interlocking parts and nerve roots associated with thespinal column, can result in back pain due to various reasons. Such backpain may result from the degeneration of disks due to age, disease, orinjury. Further, vertebral bodies may be compromised due to disease ordefects, such as a tumor, or injury, such as fracture.

In certain cases, it may be necessary to remove or replace one or moreof the vertebral bodies or disks to alleviate pain or regain spinalfunctionality. Replacement of a vertebral body is typically required dueto an unstable burst fracture, severe compression facture, or tumordecompression.

A vertebral body replacement procedure typically involves the removal ofthe disks above and below the compromised vertebral body along with allor a portion of the vertebral body. In place of the removed elements, astrut graft and plate are used make the vertebrae above and below thereplaced vertebral body grow together and become one bone. Because theintention of a spinal fusion procedure utilized along with vertebralbody replacement is to create solid bone in the area that is excised,the spacer that is inserted to restore normal height may be configuredto enhance bone in-growth, which may be enhanced by the addition of bonegrowth material.

In a vertebral body replacement procedure, the vertebral body ispartially or entirely replaced by a vertebral prosthesis. Severalvertebral prosthesis designs are known in the art. One such vertebralprosthesis design is shown in U.S. application Ser. No. 10/686,998,titled “Vertebral Prosthesis,” which is incorporated by reference hereinin its entirety.

When a vertebral prosthesis is utilized to replace a vertebral body, aspinal fixation system may be utilized to stabilize the adjacentvertebrae. Such a spinal fixation system may include a plate designed tobe attached to the adjacent vertebrae with bone screws to lock theadjacent vertebrae into position relative to one another. The spinalfixation system may be utilized because the vertebral prosthesis is notconfigured to provide the stability necessary for fusing the prosthesiswith the adjacent vertebrae.

The use of a vertebral prosthesis along with a supplemental spinalfixation system presents certain challenges. Depending on the loadcarried by the vertebral prosthesis, the prosthesis can collapse intothe adjacent bone. Further, the bone screws utilized to attach thespinal fixation plate to the adjacent vertebrae may migrate over time,decreasing the effectiveness of the spinal fixation.

It would be advantageous to provide a vertebral body replacement systemthat includes a vertebral prosthesis and spinal fixation system that aredesigned to work in conjunction with one another to address one or moreof the above identified challenges presented by current systems. Itwould also be advantageous to provide a vertebral body replacementsystem that may be utilized without a supplemental spinal fixationsystem while still providing the spinal fusion functionality.

It would be desirable to provide a system and/or procedure that providesone or more of these or other advantageous features. Other features andadvantages will be made apparent from the present specification. Theteachings disclosed extend to those embodiments that fall within thescope of the appended claims, regardless of whether they accomplish oneor more of the above-identified needs.

SUMMARY OF THE INVENTION

The invention relates to a spinal implant system having a vertebralprosthesis adapted to be placed adjacent a vertebra. The system furtherincludes at least one bone screw and a spinal fixation device coupled tothe prosthesis by the bone screw. The bone screw extends through atleast a portion of the vertebra.

The invention further relates to a vertebral prosthesis for replacing acompromised vertebra. The prosthesis includes a shaft having an endplateat one end, and an anchor extending from the endplate. The anchor isadapted to extend into an adjacent vertebra and includes an aperturesized to receive a bone screw.

The invention further relates to a spinal fixation system having avertebral prosthesis with a shaft. The height of the shaft is adjustableafter implantation in a patient without adding or removing components toor from the shaft. An anchoring mechanism is coupled to the shaft. Thesystem further includes a spinal fixation device and a bone screw. Thebone screw attaches the spinal fixation device to the anchoringmechanism.

The invention further relates to a method of implanting a vertebralprosthesis. The method includes the steps of opening an aperture in apatient to permit access to a first vertebra located adjacent to asecond vertebra, removing at least a portion of the first vertebra, andinserting a vertebral prosthesis into the space created by the removalof the portion of the first vertebra. The method further includes thesteps of providing a bone screw and a spinal fixation device, couplingthe fixation device to the vertebral prosthesis with the bone screw suchthat the bone screw extends through at least a portion of the secondvertebra, and closing the aperture.

The invention further relates to a method of implanting a vertebralprosthesis. The method includes the steps of opening an aperture in apatient to permit access to a first vertebra located adjacent to asecond vertebra, removing at least a portion of the first vertebra,providing a vertebral prosthesis having an anchoring mechanism, andcreating a cavity in the second vertebra sized to receive the anchoringmechanism. The method further includes the steps of inserting thevertebral prosthesis into the space created by the removal of theportion of the first vertebra, impacting the anchoring mechanism intothe cavity, coupling the prosthesis to the second vertebra with a bonescrew, and closing the aperture.

The invention is capable of other embodiments and of being practiced orbeing carried out in various ways. Alternative exemplary embodimentsrelate to other features and combinations of features as may begenerally recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingdrawings, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is a perspective view of a vertebral prosthesis;

FIG. 2 is an exploded perspective view of a vertebral prosthesis andspinal fixation system;

FIG. 3 is a perspective view of a vertebral prosthesis and spinalfixation system;

FIG. 4 is a sectional view of a vertebral prosthesis assembled togetherwith a spinal fixation system;

FIG. 5 is an elevation view of the components of a vertebral prosthesisprior to assembly;

FIG. 6 is an elevation view of the components of a partially assembledvertebral prosthesis;

FIG. 7 is an elevation view of the components of a partially assembledvertebral prosthesis;

FIG. 8 is an elevation view of an assembled vertebral prosthesis;

FIG. 9 is an elevation view of a vertebral prosthesis and spinalfixation system prior to assembly with one another;

FIG. 10 is an elevation view of a vertebral prosthesis and spinalfixation system after assembly with one another;

FIG. 11 is a perspective view of a vertebral prosthesis and spinalfixation system inserted into a spine;

FIG. 12 is a perspective view of a vertebral prosthesis and spinalfixation plate inserted into a spine; and

FIG. 13 is a perspective view of a vertebral prosthesis inserted into aspine.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, according to an exemplary embodiment, a vertebralprosthesis 10 includes a pair of endplates, shown as upper endplate 12and lower endplate 14. The endplates 12, 14 are connected to one anotherby a shaft 16.

Referring to FIG. 2, the shaft 16 may include several components,including upper portion 18 and lower portion 20. A locking ring 22 maybe held in place by a washer 24 and used to connect lower portion 20 toupper portion 18. In the embodiment shown in FIG. 2, the lower portion20 is received within cylindrically shaped upper portion 18 and fixed inplace by a fixation device, shown a screw 28. The use of the lockingring 22 and screw 28 permits the height of shaft 16 to be adjusted asdesired by the surgeon.

Further referring to FIG. 2, in an exemplary embodiment, locking ring 22locks the upper portion 18 and lower portion 20 into position relativeto each other via interlocking teeth 30 on both the locking ring 22 andlower portion 20 that engage one another when screw 28 is tightened, asindicated in FIG. 4.

Further referring to FIG. 2, a spinal fixation system according to anexemplary embodiment is shown as including a spinal fixation device,shown as, but not limited to, locking plate 32, and a number of bonescrews 34. The bone screws 34 are configured to extend through a numberof apertures in the locking plate 32, shown as holes 36 and slot 38. Thespinal fixation device, while shown as locking plate 32 in theembodiment of FIG. 2, may also be a rod or another device suitable toprovide for fixation of vertebrae.

Referring to FIGS. 1 and 4, the vertebral prosthesis includes a numberof apertures configured to receive and be secured to bone screws 34. Inparticular, the shaft 16 includes two apertures 40, and the endplates,12, 14 each have an anchoring mechanism or anchor, shown as, but notlimited to, anchors 42, 44, each having a body portion and a threadedaperture 46 configured to receive a bone screw 34. The bone screws 34are shown as screws, but may also take the form of bolts or otherattachment mechanisms in alternative embodiments.

Referring to FIGS. 3 and 4, the locking plate 32 may be secured to thevertebral prosthesis 10 by screwing the bone screws 34 into thecorresponding apertures 40, 46 in the vertebral prosthesis 10. The bonescrews 34 and apertures 40, 46 are configured to engage one another suchthat the bone screws 34 may be adjustably secured to the vertebralprosthesis 10. The bone screws 34 may be self-drilling as is known inthe art or may have a cannulated design configured to be used with adrill and driver as described in U.S. application Ser. No. 10/864,673,titled “Spinal Fixation System,” which is incorporated herein byreference in its entirety.

In an exemplary embodiment, the endplates are configured to be threadedor screwed on and off of the shaft 16 of the vertebral prosthesis 10 sothat endplates 12, 14 may be quickly and easily removed and installeddepending on the desired configuration. In other embodiments, theendplates 12, 14 and shaft 16 may be snapped on or twist-locked onto oneanother. The surgeon may have the choice of several endplates dependingon the desired final configuration of the vertebral prosthesis system.

Referring to FIGS. 5-8, the vertebral prosthesis 10 may be assembled byplacing the locking ring 22 and washer 24 onto the upper portion 18,followed by inserting the lower portion 20 into the upper portion 18 tothe extent necessary to achieve the desired distance between theendplates 12, 14. The screw 28 may then be inserted into the lockingring 22 in order to releasably secure the lower portion 20 relative tothe upper portion 18. If necessary, the height may be further adjustedby loosening the screw 28 and changing the position of the lower portion20 relative to the upper portion 18, followed by retightening of thescrew 28.

FIGS. 9 and 10 illustrate the attachment of the locking plate 32 to thevertebral prosthesis 10. The bone screws 34 are inserted through theapertures in the locking plate 32 and screwed into the correspondingapertures in the vertebral prosthesis 10. Although the use of four bonescrews 34 is shown, in other embodiments, a different number of bonescrews 34 may be utilized.

Referring to FIGS. 3, 10, and 11, the outer bone screws 34 areconfigured to engage the anchors 42, 44. To aid in such engagement, asegment 48 of the bone screws 34 may be provided with different threads,such as threads having a different thread pitch, intended to mate withthe interior threaded portions of the anchors 42, 44. A similar approachmay be utilized with the bone screws 34 that attach to the shaft 16.

FIG. 11 depicts vertebral prosthesis 10 installed in a spine inaccordance with one exemplary embodiment. In the example shown, adiseased or injured vertebra has been removed and the vertebralprosthesis 10 has been inserted between a superior vertebra 52 and aninferior vertebra 50. Further, the two natural disks adjacent theremoved vertebra have been excised to permit the inferior and superiorvertebrae 50, 52 to be fused together as one structure with thevertebral prosthesis 10.

Attachment of the locking plate 32 to the vertebral prosthesis 10 isintended to create a unified vertebral prosthesis and spinal fixationsystem that provides superior support, as compared to a vertebralprosthesis and spinal fixation system that are not interconnected withone another. Additionally, the upper and lower outer bone screws 34extend through the bone of inferior vertebra 50 and superior vertebra 52to provide additional support. The unified prosthesis and fixationsystem may eliminate the need for spikes or other engaging mechanismsextending from the endplates that would typically be used to aid in theengagement between the prosthesis and the adjacent vertebrae because theprosthesis 10 is instead fixed in place by the bone screw 34 extendingthrough the adjacent vertebrae 50, 52 and locking plate 32.

The system depicted in FIG. 11 is intended to address the issue ofspinal fixation device bone screw migration. By anchoring the bonescrews 34 used to attach the locking plate 32 into the vertebralprosthesis 10, the bone screws are intended to be less prone tomigration within the vertebrae 50, 52, as compared to a spinal fixationdevice attached only to vertebrae. Note how the anchors 42, 44 extendinto the adjacent vertebrae 50, 52 to permit the engagement of both boneand the anchors 42, 44 by the upper and lower outer bone screws 34.Further, the locking plate 32 provides an additional longitudinalsupport between the vertebrae 50, 52. The additional support is intendedto reduce the incidence of the vertebral prosthesis collapsing into oneor both of the adjacent vertebrae 50, 52 due to the vertebral prosthesiscarrying all of the load between the adjacent vertebrae 50, 52.

Further referring to FIG. 11, the spacing between the apertures inlocking plate 32 is intended to aid the surgeon in fastening the bonescrews 34 into the prosthesis 10. The two lower apertures in the lockingplate 32 may be spaced to correspond to the spacing between the twolower apertures in the prosthesis 10 so that once the lower interiorbone screw 34 is inserted through the locking plate 32 and into theshaft, the lower outer bone screw 34 may be drilled into the inferiorvertebra 50 and automatically guided through the aperture in anchor 44due to the spacing between the apertures in the locking plate beingconfigured to automatically provide the proper spacing between bonescrews 34.

The slot 38 in the locking plate 32 (see FIG. 3) provides flexibilitywith respect to the adjustable height of vertebral prosthesis 10. Whenthe height of the vertebral prosthesis 10 is changed during surgery, thedistance between the upper and lower bone screws 34 is also changed. Theslot 38 permits variability in the placement of bone screws so that asingle locking plate 32 may be utilized with one adjustable heightvertebral prosthesis, rather than requiring a variety of differentlyconfigured locking plates 32.

FIG. 11 depicts the vertebral prosthesis 10 in use with a lateralthoracolumbar locking plate. Referring to FIG. 12, the system may alsobe utilized with an anterior placement of the locking plate 32, such asmay be utilized in the treatment of cervical burst fractures. Note thatin other embodiments of the invention, additional bone screws may beutilized to attach the spinal fixation device to the vertebralprosthesis. The additional bone screws may extend through otherapertures in the shaft or anchors, or may attach to additional anchoringmechanisms extending from the endplates.

The vertebral prosthesis, spinal fixation plate, and bone screwsdescribed herein may be composed of a titanium alloy, although othermaterials may also be suitable. The other materials may be ceramic,composite, or metallic, and may be absorbable or bioactive. Further, thevertebral prosthesis, spinal fixation plate, and bone screws may havedifferent configurations in alternative embodiments still within thescope of the present invention.

Referring to FIG. 13, in an alternative embodiment, the vertebralprosthesis 10 may be attached to adjacent vertebrae 50, 52 with bonescrews 34 without use of a locking plate. The bone screws 34 areattached to both the vertebral prosthesis and the inferior and superiorvertebrae 50, 52 and therefore provide the necessary structuralstability for spinal fusion to occur without the use of a supplementalspinal fixation system such as a locking plate. In other embodiments,additional bone screws may be utilized to provide the desired structuralstability and may extend through additional apertures in the anchors orthorough additional anchoring mechanisms extending from the endplates.

A diseased or damaged vertebra may be replaced or reconstructed usingthe following exemplary procedure. As an initial matter, it must bedetermined that the vertebra in question must be replaced. The reasonsfor replacement may include a lumbar burst fracture or a cervicalfracture. Prior to operating, a vertebral prosthesis will be chosen onthe basis of pre-operative sizing. Depending on the location of thevertebra to be replaced or reconstructed, the surgeon will create anaperture in the patient using a lateral or anterior approach as desired.When spinal fusion is desired, the natural disks above and below thecompromised vertebra will be excised along with the vertebra inquestion, removing the bone infringing on the nervous structures as wellas most of the vertebral body.

The sizing of the vertebral prosthesis will then be confirmedintraoperatively. The inferior and superior vertebrae 50, 52 will beprepared to accept the anchors 42, 44, such as by utilizing a high speedburr to cut a channel into each of the adjacent vertebrae 50, 52 toaccept the anchors 42, 44. The vertebral prosthesis may then be placedinto position between the inferior and superior vertebrae 50, 52 and thebone screws 34 used to attach the locking plate 32 to the vertebralprosthesis 10, creating the combined vertebral prosthesis and spinalfixation system. Pedicle screws (not shown) may be utilized to furtherstabilize the vertebral prosthesis, such as by placing pedicle screwsthrough the pedicles and into a pedicle screw attachment point on thevertebral prosthesis as shown in U.S. application Ser. No. 10/686,998.

After the vertebral prosthesis has been placed into the spine, it may benecessary to adjust the height prior to securing the prosthesis with thebone screws. The height may be adjusted in situ by loosening the screw28 to permit the upper and lower portions 18, 20 of the shaft 16 to beadjusted relative to one another to adjust the height of the prosthesisand retightening the screw 28 to lock the shaft at the desired height.

After insertion of the vertebral prosthesis and locking plate, bonegraft or other supplementation may be placed around the vertebralprosthesis to aid in the fusion of the inferior and superior vertebrae.Further, bone graft or a supplement may be placed into the shaft priorto surgery to enhance bone ingrowth as desired. The endplates 12, 14 mayhave a lattice or mesh design in order to promote bone ingrowth forfusion purposes. Finally, the aperture in the patient is closed tocomplete the surgical procedure.

While the detailed drawings and specific examples given herein describevarious exemplary embodiments, they serve the purpose of illustrationonly. It is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangements ofcomponents set forth in the preceding description or illustrated in thedrawings. For example, the vertebral prosthesis is shown as having twobone screws inserted into the shaft and two bone screws inserted intothe anchoring mechanisms, but other configurations are contemplated andare within the scope of the invention. Further, the anchor design maytake different shapes and sizes depending on the type and configurationof bone screws used to attached the locking plate to the vertebralprosthesis. Furthermore, other substitutions, modifications, changes,and omissions may be made in the design, operating conditions, andarrangements of the exemplary embodiments without departing from thescope of the invention as expressed in the appended claims.

1. A spinal implant system for replacing a damaged vertebra in a spinalfusion procedure, comprising: a vertebral prosthesis adapted to beplaced at the site of an excised vertebra between two adjacentvertebrae, the vertebral prosthesis comprising a shaft having two endsand an endplate at each end, wherein the shaft is rigid and theendplates are locked to the shaft to create a rigid structure suitablefor a spinal fusion procedure in which the vertebrae adjacent to thevertebral prosthesis are fused together with the vertebral prosthesis asone rigid structure; a bone screw; an anchor extending from at least oneof the endplates wherein the anchor is positioned on the endplate suchthat it is configured to extend into one of the adjacent vertebrae; anda spinal fixation device coupled to the prosthesis by the bone screw,wherein the bone screw is adapted to extend through at least a portionof one of the adjacent vertebrae; wherein the anchor comprises a bodyportion and an aperture configured to receive the bone screw when withinthe adjacent vertebra, and further wherein the aperture is threaded. 2.The spinal implant system of claim 1, wherein the vertebral prosthesiscomprises a longitudinal axis, and further wherein the anchor extendsfrom at least one of the endplates along the longitudinal axis of thevertebral prosthesis.
 3. The spinal implant system of claim 1, whereinthe bone screw comprises a first threaded portion having a first threadpitch suitable for drilling through and engaging one of the adjacentvertebrae and a second threaded portion having a second thread pitchsuitable for engaging the threaded aperture.
 4. The spinal implantsystem of claim 1, wherein the vertebral prosthesis is configured to beexpanded after being placed between the two adjacent vertebrae.
 5. Thespinal implant system of claim 1, wherein the spinal fixation device isa locking plate comprising at least one aperture sized to receive thebone screw.
 6. The spinal implant system of claim 1, further comprising:a second anchor extending from the other of the endplates and configuredto extend into the other of the adjacent vertebrae; and a second bonescrew coupling the spinal fixation device to the second anchor.
 7. Thespinal implant system of claim 1, wherein the prosthesis includes apedicle screw attachment point and further comprising a pedicle screwconfigured to attach the prosthesis to a pedicle.
 8. A vertebralprosthesis system for replacing a compromised vertebra, comprising: avertebral prosthesis comprising a shaft having an endplate at each endwherein the shaft is rigid and the endplates are locked to the shaft tocreate a rigid structure suitable for a spinal fusion procedure in whichthe vertebrae adjacent to the vertebral prosthesis are fused togetherwith the vertebral prosthesis as one rigid structure; and an anchorextending from one of the endplates, the anchor adapted to extend intoan adjacent vertebra and comprising an aperture sized to receive a bonescrew, wherein the aperture is threaded; and a bone screw having a firstthread portion and a second thread portion each having a thread pitchsuitable for engaging the adjacent vertebra and third thread portionhaving a thread pitch suitable for engaging the threaded aperture,wherein the third thread portion is located between the first threadportion and the second thread portion and the thread pitch of the thirdthread portion is different than the thread pitch of both the firstthread portion and second thread portion.
 9. The vertebral prosthesissystem of claim 8, wherein the thread pitch of the first thread portionis the same as the thread pitch of the second thread portion.
 10. Thevertebral prosthesis system of claim 8, wherein the vertebral prosthesisis configured to be expanded after being placed adjacent the vertebra.11. The vertebral prosthesis system of claim 8, further comprising aspinal fixation device having at least one aperture sized to receive thebone screw.
 12. The vertebral prosthesis system of claim 11, furthercomprising: a second anchor extending from the other of the endplatesand adapted to extend into a second adjacent vertebra; and a second bonescrew coupling the spinal fixation device to the second anchor.
 13. Thevertebral prosthesis system of claim 8, wherein the prosthesis includesa pedicle screw attachment point and further comprising a pedicle screwconfigured to attach the vertebral prosthesis system to a pedicle.
 14. Aspinal fixation system for replacing a damaged vertebra, comprising: avertebral prosthesis adapted to be placed at the site of an excisedvertebra between two adjacent vertebrae, the vertebral prosthesiscomprising a shaft having two endplates, wherein the height of the shaftis adjustable after implantation in a patient without adding or removingcomponents to or from the shaft and wherein the shaft is rigid and theendplates are locked to the shaft to create a rigid structure suitablefor a spinal fusion procedure in which the vertebrae adjacent to thevertebral prosthesis are fused together with the vertebral prosthesis asone rigid structure; an anchoring mechanism coupled to one of theendplates; a spinal fixation device; and a bone screw, wherein the bonescrew attaches the spinal fixation device to the anchoring mechanism.15. The spinal fixation system of claim 14, wherein the anchoringmechanism comprises a body portion and an aperture configured to beattached to the bone screw.
 16. The spinal fixation system of claim 15,wherein the aperture is threaded.
 17. The spinal fixation system ofclaim 16, wherein the bone screw comprises a first threaded portionhaving a first thread pitch suitable for drilling through and engagingone of the adjacent vertebrae and a second threaded portion having asecond thread pitch suitable for engaging the threaded aperture.
 18. Thespinal fixation system of claim 14, wherein the spinal fixation deviceis a locking plate comprising at least one aperture sized to receive thebone screw.
 19. The spinal fixation system of claim 14, wherein theendplates are detachable from the shaft.
 20. The spinal fixation systemof claim 14, further comprising: a second anchoring mechanism extendingfrom the other of the endplates; and a second bone screw coupling thespinal fixation device to the second anchor.
 21. The spinal fixationsystem of claim 14, wherein the prosthesis includes a pedicle screwattachment point and further comprising a pedicle screw configured toattach the prosthesis to a pedicle.